The invention relates to low dielectric constant layers in semiconductor processing for use in various applications. More specifically, the invention relates to the UV treatment for repair of process-induced damage of low dielectric constant dielectric materials in, for example, damascene processing.
Ultrafine feature sizes and high performance requirements have necessitated the integration of low dielectric constant (low-k) insulating materials, that are mechanically weaker than previous generation materials, into semiconductor devices. The inherently weak nature of the low-k dielectric material can pose significant challenges for downstream electronic-packaging processes and material compatibility.
Low-k materials are, by definition, those semiconductor-grade insulating materials that have a dielectric constant (“k”) lower than that of SiO2, i.e., 3.9. Various types of low-k materials can have dielectric constants ranging from about 3.8-3.6 (e.g., fluorosilicate glass (FSG)), to less than about 3.2 (e.g., (carbon doped oxide (CDO)), to as low as 2.2 (e.g., spin-on glass (SOG)) or even lower, and encompass low-k dielectrics referred to as “ultra low-k” (ULK) and “extreme ultra low-k” (ELK). In many CDO carbon-containing low-k implementations, such as are described herein, suitable carbon-containing low-k materials have a dielectric constant of about 2.7 or lower. To further reduce the size of devices on integrated circuits, it has become necessary to use conductive materials having low resistivity and insulators having low dielectric constants to reduce the capacitive coupling between adjacent metal lines. Low-k materials are being integrated into the devices to improve device performance and allow for device scaling.
Low-k materials are less dense than standard insulating materials such as SiO2. This introduces a host of process integration and material compatibility difficulties. The balance between maintaining the film's integrity and integrating it properly and performing the necessary stripping, cleaning, and conditioning gets increasingly precarious. Patterning processes (etching, stripping, deposition, and cleaning) can also have a drastic impact on the integrity of carbon-containing low-k materials, in particular SiOC-based low-k materials.
The properties that give carbon-containing low-k dielectric materials their desirable low dielectric constants are the very same properties that are leading to significant integration challenges. Carbon-containing low-k materials achieve lower dielectric constants through the incorporation of non-polar covalent bonds (e.g., from the addition of carbon) and the introduction of porosity to decrease film density. Introducing porosity or the incorporation of terminal bonds, such as Si—CH3, breaks the continuity of the rigid Si—O—Si lattice of traditional oxides, yielding a lower dielectric constant film that is both mechanically and chemically weaker. Because of the mechanical weakness, carbon-containing low-k films are susceptible to kinetic plasma damage that can undesirably densify the film and thus increase the film's effective k value.
Furthermore, chemical plasmas can modify carbon-containing low-k films where bonds such as Si—CH3 are readily broken. The susceptibility of carbon-containing low-k materials to plasma modification poses a serious integration challenge since plasma processes are routinely used to etch, clean, and deposit films in the manufacturing of a semiconductor device. Moreover, in damascene processing, prior to metal barrier deposition, process induced carbon-containing low-k dielectric damage can be incurred from etch, dry resist strip, wet cleaning and dry cleaning. Carbon-containing low-k materials are also susceptible to the intercalation of plasma species, residues, solvents, moisture, and precursor molecules that can either adsorb into, outgas from, or chemically modify the film.
Damage to the carbon-containing low-k dielectric material on the sidewalls of the via trenches or in the inter-layer dielectric (ILD) regions during copper (Cu) damascene processing can compromise the integrity of dielectric spacing, leading to increased leakage, higher capacitance, and reduced performance and reliability. The damaged low-k layers can absorb moisture which remains trapped in the dielectric. This can oxidize the barrier material leading to Cu diffusion. Damage of the low-k dielectric material is linked to the loss of methyl groups (CH3) in the film during processing. Thus, dielectric repair to prevent the unwanted absorption of moisture is important.
Carbon depletion occurs when, for example, a Si—CH3 bond is broken leaving a silicon dangling bond. Reaction with absorbed water results in the formation of silanol (Si—OH) groups. Slurry from chemical mechanical polishing (CMP) can also chemically remove carbon groups on the surface of the low-k dielectric film. Again, a reaction with the water present in the CMP slurry results in the formation of highly polarizable silanol (Si—OH) groups, which leads to an increase in k value for the damaged portion of the film, increasing the effective k value of the dielectric significantly.
Because of this, semiconductor manufacturers have developed methods to eliminate carbon depletion or replenish (repair) the depleted carbon. One method is the use of chemicals called “Toughening Agents” (TA) to repair carbon depletion damage. Another method is to use sacrificial capping layers to protect the low-k films from carbon depletion. However, both methods narrow the required process window and lead to higher manufacturing costs. Furthermore, an increase k effective may still result. Thus, improved methods for low-k dielectric repair in semiconductor processing are needed.